Vibration damper having a buffer spring

ABSTRACT

A vibration damper is disclosed which includes a damper tube filled with a damping medium; a piston rod which can move in an oscillating and reciprocal manner in the damper tube and one end of which protrudes into the damper tube and which comprises at this end a piston rod extension and a shoulder. A piston divides the interior of the damper tube into a working chamber remote from the piston rod and a piston rod-side working chamber and which is disposed coaxially with respect to the piston rod extension and comprises restrictor openings and at least one spring washer covering these restrictor openings in each working chamber. A buffer spring is disposed in the piston rod-sideworking chamber.

BACKGROUND OF THE INVENTION

The invention relates to a vibration damper having: a damper tube filledwith a damping medium; a piston rod which can move in an oscillating andreciprocal manner in the damper tube and one end of which protrudes intothe damper tube and which comprises at this end a piston rod extensionand a shoulder; a piston which divides the interior of the damper tubeinto a working chamber remote from the piston rod and a piston rod-sideworking chamber and which is disposed coaxially with respect to thepiston rod extension and comprises restrictor openings and at least onespring washer covering these restrictor openings in each workingchamber; a buffer spring disposed in the piston rod-side workingchamber; and also a spring collar which is disposed in the pistonrod-side working chamber and has a first support surface supporting thebuffer spring and a second support surface for the at least one springwasher disposed in the piston rod-side working chamber.

A vibration damper of this type is known from DE 196 26 143 C2. In thisknown vibration damper a buffer in the form of a buffer spring isdisposed in the upper working chamber concentrically with respect to thepiston rod. The buffer spring is centred in the guiding direction of thepiston rod by a spring collar which can possibly comprise an inner slipring in order to allow only minimal frictional forces to occur duringrelative movement with respect to the piston rod. The other end of thebuffer spring lies against a bearing of a disc body. This disc bodyforms the spring collar in terms of the present invention and is bracedon a pin of the piston rod together with the piston. The disc bodycomprises, on its side remote from the buffer spring, a support surfacefor the spring washers disposed in the piston rod-side working chamber.

A disadvantage in the known vibration damper resides in the fact thatforces exerted by the buffer spring onto the disc body (the springcollar) are introduced directly into the working piston via the pistonrod-side spring washers. As a result, the damping characteristic of thedamping piston is negatively influenced. Furthermore, the forces exertedby the buffer spring onto the disc body (the spring collar) flow intothe pin of the piston rod via the working piston which can lead toproblems in terms of stability in the region of the pin. In extremecases, deformation or even separation of the pin can occur in the caseof high buffer forces.

SUMMARY OF THE INVENTION

The object of the invention is to develop a vibration damper of the typementioned in the introduction such that a force exerted by the bufferspring onto the spring collar does not cause the above-mentioneddisadvantages and an installation space of maximum length is availablefor the buffer spring.

This object is achieved in accordance with the invention by virtue ofthe fact that the spring collar comprises a stepped bore which has afirst bore section having a small diameter and a second bore sectionhaving a larger diameter, wherein the first bore section is allocated tothe piston rod extension and the second bore section is allocated to theend of the piston rod, and that the spring collar is connected to thepiston rod in a non-positive and/or positive locking manner so that aforce exerted by the buffer spring onto the spring collar is introduceddirectly into the piston rod.

By virtue of the fact that a non-positive and/or positive lockingconnection is provided between the spring collar and the piston rod, aforce exerted by the buffer spring onto the spring collar is introduceddirectly into the piston rod without the force being introduced onto thepiston rod-side spring washers of the working piston and thus into theworking piston itself. In this manner, forces emanating from the bufferspring do not have a disruptive influence on the damping characteristicof the working piston. Furthermore, high buffer forces are preventedfrom being introduced into the piston rod extension via the workingpiston. In this manner, possible deformations, damage or a possibleseparation of the piston rod extension are obviated.

By virtue of the fact that the spring collar comprises a stepped boreand that the bore section having the larger diameter covers the end ofthe piston rod over an axial length, a small axial installation heightfor the arrangement consisting of the piston rod, spring collar andbuffer spring is achieved. For this purpose, the second bore section,i.e., the bore section of the stepped bore having the larger diameter,is preferably provided with an inner thread which co-operates with anouter thread provided on the end of the piston rod and forms a screwconnection which is used to attach the spring collar to the piston rod.

In accordance with the invention, the spring collar is slid or screwedover the end of the piston rod with the bore section having the largerdiameter so that the spring collar is made to rest against the shoulderon the end of the piston rod by means of a stop surface which isdisposed in the transition region between the first and second boresections of the stepped bore. The spring collar on this stop surface issupported against the corresponding shoulder on the end of the pistonrod by means of the screw connection between the spring collar and theend of the piston rod.

Alternatively, the spring collar screwed onto the piston rod can liewith its end surface, remote from the piston, against a radial [lacuna]of the piston rod and can be supported on this shoulder. In thisembodiment, the entire spring collar can have a smaller extension in theradial direction, i.e., it can have smaller diameters. As a result, theannular support surface, against which the buffer spring is supported,has a smaller diameter so that a closely wound buffer spring can be usedwhich reduces the installation space and the weight.

In order to attach the piston on the piston rod extension, it is bracedin a manner known per se between the second support surface of thespring collar on the one hand and a piston nut on the other hand bymeans of the piston nut screwed onto the piston rod extension.

If the shoulder of the end of the piston rod and the corresponding stopsurface of the spring collar lying against this shoulder extend in theradial direction, then this contributes to a furtherreduction/minimisation of the axial installation height.

The spring collar in accordance with the invention comprises a guidesurface extending in the axial direction for centring and guiding thebuffer spring. In this manner, the buffer spring is reliably guided atleast in the lower region, i.e., in the region facing the workingpiston.

In order to ensure that the spring collar lies with its stop surfaceagainst the shoulder on the end of the piston rod, the second boresection of the stepped bore is provided at its end facing the first boresection with a recess. In this manner, the recess ensures that radialspace is available in which the end of the piston rod is receivedwithout the end of the piston rod in the radial direction coming intocontact with the material of the spring collar. As a result, the stopsurface of the spring collar can lie completely against the shoulder onthe end of the piston rod.

In order to apply the necessary forces to screw the spring collar withthe piston rod, a key surface is provided on the spring collar forattaching a screwing tool. Screwing tools include in particular wrenchesbut other screwing tools can be used which comprise a loop encompassingthe tool to be screwed, wherein a frictional engagement is createdbetween the loop and the tool in order to transfer the torsional momentsrequired for the screwing process.

A cost-effective buffer spring is formed as a helical spring formed ofwound steel wire. It is particularly advantageous if the thread of thespring collar, by means of which the spring collar is screwed to thepiston rod, has a pitch oriented in the opposite direction to thewinding direction of the buffer spring. If the buffer spring formed as ahelical spring is a spring having a right winding, then the springcollar has a left thread and vice-versa. This is advantageous in thattorsional moments exerted by the buffer spring onto the spring collar donot cause the spring collar to become unscrewed but rather act in thedirection in which the spring collar is fixedly screwed to the pistonrod. In this manner, the screw connection between the spring collar andthe piston rod cannot be undesirably loosened.

In principle it is also feasible that the thread of the spring collar,by means of which the spring collar is screwed to the piston rod, has apitch oriented in the same direction as the winding direction of thebuffer spring. In this case, an additional lock against rotation shouldbe provided on the spring collar and/or on the piston rod, by means ofwhich the spring collar is reliably prevented from being unscrewed bythe torsional moments transferred thereto by the buffer spring. The lockagainst rotation can be formed e.g., as a conventional non-positive andpositive lock against rotation as used for example for nuts in nut andscrew connections.

A preferred embodiment of the invention will be explained in detailhereinafter with the aid of the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a side, schematic and detailed illustration of anarrangement of a piston rod, working piston, spring collar and bufferspring;

FIG. 2 shows en enlarged side detailed view of the arrangement of FIG.1; and

FIG. 3 shows in detail an embodiment of the invention modified withrespect to FIGS. 1 and 2.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 illustrates an arrangement comprising a piston rod 2 having apiston rod extension 2 b, a piston 3, a spring collar 7, a buffer spring6 and a sealing and guiding unit 20, wherein the damper tube has beenleft out in order to illustrate the invention more clearly. A supportplate 21 is provided on the side of the sealing and guiding unit 20facing the working piston and the buffer spring 6 is supported againstthe support plate with its end remote from the working piston.

The axial installation length between the support plate 21 and the firstsupport surface 8 of the spring collar 7 is designated with L in FIG. 1.The point of the invention is to make this axial installation length Las large as possible and simultaneously to ensure that forces andmoments exerted by the buffer spring 6 onto the spring collar 7 areintroduced directly into the piston rod 2. Owing to the large axialinstallation space for the buffer spring 6, its length can be maximisedin the case of otherwise identical installation conditions so that therequired properties of the buffer spring 6 such as for example requiredblock gauge and required spring travel can be set to an optimal value. Alarge axial covering region is achieved in the invention, in which thespring collar 7 covers/surrounds the piston rod 2 so that theinstallation space required for accommodating the spring collar is keptsmall.

The region designated with X in FIG. 1 is illustrated in an enlargedmanner in FIG. 2. It can be clearly seen that the piston rod 2 has anouter thread at its end 2 a. The spring collar 7 comprises a steppedbore 10 which has a first bore section 11 having a small diameter d anda second bore section 12 having a large diameter D. The second boresection 12 has an inner thread which is screwed to the outer thread ofthe end 2 a of the piston rod 2. The inner thread and outer threadthreaded together 20 fix together the piston rod 2 and the spring collar7. The piston 2 is provided with restrictor openings 22. The springcollar 7 optionally includes a key surface (not shown) for attaching ascrewing tool such as for example a wrench.

The second bore section 12 comprises a recess at its end facing thefirst bore section 11. This recess ensures that the spring collar lieswith its stop surface 7 a against the shoulder 2 c of the end 2 a of thepiston rod 2.

On the working piston-side, the buffer spring 6 is supported against thefirst support surface 8 of the spring collar 7. Furthermore, the springcollar 7 comprises a second support surface 9 which faces the workingpiston and against which the spring washers 4 are supported.

The piston 3 is disposed concentrically with respect to the piston rodextension 2 b and is braced by means of the piston nut 13 which isscrewed onto an outer thread of the piston rod extension. The bracedpiston 3 is supported on the one hand against the second stop surface 9of the spring collar 7 and on the other hand against the end side of thepiston nut 13 facing the working piston.

It can be clearly seen in FIG. 2 that the spring collar 7 comprises anaxially extending support surface for the lowermost winding of thebuffer spring 6 formed as a helical spring. The inner thread of thespring collar, by means of which the spring collar is screwed to the end2 a of the piston rod 2, has a pitch oriented in the exact oppositedirection to the winding direction of the helical spring.

As can be seen particularly from FIG. 2, the second bore section 12 ofthe stepped bore 10 of the spring collar 7 and the end 2 a of the pistonrod 2 are covered in an axial manner to a large extent. This large axialcoverage ensures that the axial installation height of thearrangement—consisting of the spring collar 7, the piston rod 2 and thebuffer spring 6—is particularly small. Likewise, the fact that the stopsurface 7 a and the shoulder 2 c of the end 2 a of the piston rod 2extend precisely in the radial direction and are not disposed at anangle with respect to the longitudinal axis of the piston rodcontributes to reducing the axial installation height.

An embodiment of the invention which is modified with respect to theexemplified embodiment in accordance with FIGS. 1 and 2 is illustratedin FIG. 3. In this embodiment, the spring collar 7 is screwed, by meansof its inner thread provided in the bore section 12, onto a piston rodpin 2 f having an outer thread. The diameter of the piston rod pin 2 fis greatly reduced with respect to the diameter of the piston rod. Aradial shoulder 2 e is formed by the reduction in diameter of the pistonrod 2 to form the piston rod pin 2 f provided with the outer thread,wherein the end side 2 d, remote from the piston, of the spring collar 7screwed to the piston rod pin 2 f lies against the radial shoulder 2 e.In this embodiment of the invention, the spring collar 7 has a verysmall radial extension. By virtue of the fact that the spring collar 7is screwed, by means of its inner thread disposed in the bore section12, onto a piston rod pin 2 f reduced in diameter, the spring collar 7protrudes beyond the radial extension of the piston rod 2 only to a verysmall radial extent, except with its bearing surface for the bufferspring. The use of a particularly closely wound buffer spring 6 ispossible with this embodiment of the invention. In order for the springcollar 7 to be able to lie with its end side 2 d, remote from thepiston, against the radial shoulder 2 e of the piston rod, a recess isprovided in the region of the transition from the bore section 12 to thebore section 11.

LIST OF REFERENCE NUMERALS

-   2. Piston rod-   2 a End-   2 b Piston rod extension-   2 c Shoulder-   2 d End side-   2 e Radial shoulder-   2 f Piston rod pin-   3. Piston-   4. Spring washer-   6. Buffer spring-   7. Spring collar-   7 a Stop surface-   8. Support surface-   9. Support surface-   10. Stepped bore-   11. Bore section-   12. Bore section-   13. Piston nut-   14. Guide surface-   20. Sealing and guiding unit-   21. Support plate-   L Axial installation length-   d Diameter-   D Diameter-   X Region

1. A vibration damper comprising: a damper tube filled with a dampingmedium; a piston rod which can move in an oscillating and reciprocalmanner in the damper tube, and the piston rod having one end whichprotrudes into the damper tube and which comprises at said one end apiston rod extension and a shoulder; a piston which divides an interiorof the dumper tube into a working chamber remote from the piston rod anda piston rod-side working chamber and which is disposed coaxially withrespect to the piston rod extension, the piston defining restrictoropenings communicating with the working chamber and the piston rod-sideworking chamber; at least one spring washer adjacent the restrictoropenings and disposed in the piston rod-side working chamber; a bufferspring disposed in the piston rod-side working chamber; and a springcollar which is disposed in the piston rod-side working chamber and hasa first support surface supporting the buffer spring and a secondsupport surface for the spring washer disposed in the piston rod-sideworking chamber, the spring collar comprising a stepped bore which has afirst bore section having a small diameter and a second bore sectionhaving a larger diameter, wherein the first bore section is allocated tothe piston rod extension and the second bore section is allocated to theend of the piston rod, and the spring collar is rigidly connected to thepiston rod in a fixed manner in a first axial direction from the pistonrod to the piston rod extension so that a force exerted by the bufferspring onto the spring collar in the first axial direction is introduceddirectly into the piston rod without transmission through the piston. 2.The vibration damper as claimed in claim 1, wherein the second boresection has an inner thread forms a screw connection with an outerthread provided on the end of the piston rod for attaching the springcollar to the piston rod.
 3. The vibration damper as claimed in claim 2,wherein the buffer spring is formed as a helical spring.
 4. Thevibration damper as claimed in claim 3, wherein the thread of the springcollar, by means of which the spring collar is screwed to the pistonrod, has a pitch oriented in the opposite direction to a windingdirection of the buffer spring.
 5. The vibration damper as claimed inclaim 1, wherein the spring collar comprises a stop surface in atransition region from the first to the second bore section, said stopsurface lying against shoulder on an end of the piston rod.
 6. Thevibration damper as claimed in claim 5, wherein the shoulder of the endof the piston rod and the stop surface extend in the radial direction.7. The vibration damper as claimed in claim 1, wherein the spring collarcomprises a guide surface for centering and guiding the buffer spring.8. The vibration damper as claimed in claim 1, wherein the second boresection of the stepped bore comprises a recess at an end facing thefirst bore section.
 9. The vibration dumper as claimed in claim 1,wherein the piston rod has a radial shoulder, and the spring collar hasan end side, remote from the piston, against the radial shoulder of thepiston rod.
 10. The vibration damper as claimed in claim 1, wherein thepiston rod extension has a nut screwed thereon such that the piston isbraced between the second support surface of the spring collar and thepiston nut.